Self-supporting pleated filter

ABSTRACT

A self-supporting, pleated filter, and method of making the same. The method includes forming a plurality of pleats in a filter media that extend along a front face and a rear face. The pleats include a plurality of pleat tips and sloping side surfaces generally perpendicular to the direction of pleating. At least one planar reinforcing strip oriented in the direction of pleating is bonded to the pleat tips on the front face. At least one reinforcing member is positioned along the rear face of the filter media. The filter media is then cut to size. Frame members are applied for some applications. The reinforcing member may be a reinforcing strip oriented in the direction of pleating and bonded to the rear face of the filter media prior to the step of forming the plurality of pleats. A second planar reinforcing strip may optionally be bonded to the reinforcing strip pleat tips. The reinforcing member, the first reinforcing strip and the second reinforcing strip can be aligned to form a truss structure. Alternatively, reinforcing strips oriented perpendicular to the direction of pleating are bonded to the rear face of the filter media prior to the step of forming the pleats. In another embodiment, a reinforcing member is applied to the rear face of the filter media after the pleats have been formed. The reinforcing member is positioned along at least one of the sloping side surfaces of the pleats on the rear face in a direction perpendicular to the direction of pleating. In another embodiment, a scrim is positioned along the rear face of the filter media. The scrim can be bonded to the frame members, the filter media and/or a portion of the frame members extend over a perimeter of the scrim to secure it to the pleated filter.

This application is a divisional application of U.S. application Ser.No. 09/354,416, filed Jul. 15, 1999, now U.S. Pat. No. 6,521,011 thedisclosure of which is herein incorporated by reference.

TECHNICAL FIELD

The present invention is directed to a method of making aself-supporting, pleated filter with reinforcing structures that resistspleat deformation, and in particular, to a fully automated method ofmaking a pleated filter for air filtration.

BACKGROUND OF THE INVENTION

The surface area of filter media is a major factor in determining flowresistance (i.e., pressure drop) and loading capacity of a pleatedfilter. The surface area of a pleated filter media is determined by thesize of the pleated filter, the depth of the pleats, and the pleatdensity. Since the external dimensions of pleated filters are oftenrestricted by the particular application, the number of pleats per inch(pleat density) can be increased to improve filtration performance.

The ability of air filter media to withstand operating pressures istypically dependent upon the pleat count, the pleat depth and thestiffness of the filter media. The filter media can become unsteady whenair pressure is applied to one side. In the event the pleats deform orcollapse, a portion of the surface area can be reduced and the pressuredrop across the filter element will increase, further increasing theforce applied to the filter media.

U.S. Pat. No. 5,618,324 (Sommer, et al.) discloses a self-supporting,accordion folded filter element that includes a planar reinforcingstrips bonded to the pleat tips by an adhesive.

A filter element available from Columbus Industries available under theproduct designation Microshield utilizes a glue bead to providelongitudinal stabilization. The glue bead is applied before the foldingof the filter media and connects the folds with one another at the pointof application. However, the glue beads require a large quantity of meltbonding agent, resulting in increased cost. Additionally, the glue beadsrequire the pleats to be closely spaced, limiting application of thistechnique to pleat counts generally greater than about six pleats perinch.

U.S. Pat. No. 4,547,950 (Thompson) discloses a method of spacing thefolds of a pleated filter media using a tapered assembly comb havinguniformly spaced teeth. Subsequently, a rigid divider is inserted intothe separated and folded media to produce a uniformly spaced filtermedia. Thompson does not disclose automated filter elementmanufacturing.

Therefore, there is a need for an automated method of manufacturing apleated filter that has good flow characteristics and exhibitssufficient stability so that the pleats do not collapse or deform whensubjected to operating pressure.

SUMMARY OF THE INVENTION

The present invention is directed to a self-supporting, pleated filterfor air filtration, and method of making the same. The method of thepresent invention provides for assembly of the pleated filter by anautomated process at a high rate of manufacturing. The pleated filter ofthe present invention can be use with or without a reinforcing framestructure. The present method and apparatus may utilize conventionalfilter media, electret media, or a variety of other media suitable forair filtration, such for furnace applications.

In one embodiment, the method of making the self-supporting pleatedfilter includes forming a plurality of pleats in a filter media thatextend along a front face and a rear face. The pleats include aplurality of pleat tips and sloping side surfaces generallyperpendicular to the direction of pleating. At least one reinforcingstrip oriented in the direction of pleating is bonded to the pleat tipson the front face to form a pleated filter. At least one reinforcingmember is positioned along the rear face of the filter media. The filtermedia is then cut to size. Frame members are optionally applied for somefiltration applications. Alternatively, the self-supporting pleatedfilter can be used without a frame or inserted into a permanent framethat permits the media to be easily changed.

In one embodiment, the step of positioning at least one reinforcingmember includes locating one or more elongated reinforcing membersoriented in the direction of pleating to the rear face of the filtermedia prior to the step of forming the plurality of pleats. A pluralityof pleats are then formed in the reinforcing member during the step offorming the pleats in the filter media. The pleats formed in thereinforcing member define reinforcing member pleat tips. A secondreinforcing strip may optionally be bonded to the reinforcing memberpleat tips. In one embodiment, the reinforcing member, the firstreinforcing strip and the second reinforcing strip are aligned to form atruss structure. The reinforcing member can optionally be bonded to thefilter media.

In another embodiment, the plurality of reinforcing members orientedperpendicular to the direction of pleating are located on the rear faceof the filter media prior to the step of forming the pleats. A pluralityof pleats are formed in the reinforcing member during the step offorming the pleats in the media. A second reinforcing strip oriented inthe direction of pleating may be bonded to the pleat tips of the rearface over the reinforcing member.

In another embodiment, the reinforcing member is inserted into thepleats on the rear face of the filter media after the pleats have beenformed. At least one reinforcing member is positioned along at least oneof the sloping side surfaces of the pleats on the rear face in adirection perpendicular to the direction of pleating. A secondreinforcing strip oriented in the direction of pleating may optionallybe bonded to the pleat tips on the rear face over the reinforcingmember.

In another embodiment, a scrim is positioned along the rear face of thefilter media. The scrim can be bonded to the pleat tips along the rearface. In one embodiment, a portion of the frame members extend over aperimeter of the scrim to secure it to the pleated filter. A scrimrefers to a porous mesh, netting or screen. The scrim can be constructedfrom various metals, plastics or paper-based products.

In another embodiment, a scrim can be substituted for the reinforcingstrips located along the front face. The scrim is bonded to the pleattips on the front face to form a pleated filter. Any of the reinforcingmembers disclosed herein can be used along the rear face of the pleatedfilter.

The present method may also include the step of heat setting one or moreof the filter media and the reinforcing members after forming thepleats. The step of applying the frame members typically includespositioning a portion of the frame members onto a portion of the frontface and, the rear face of the filter media. An adhesive is typicallyapplied between the perimeter of the filter media and the frame members.The present method may be performed using a fully automated system. Thereinforcing members and reinforcing strips may be constructed fromvarious paperboard products, polymeric materials such as films, ormetals configured as elongated strips, scrims, strands or filaments.

The present invention is also directed to a self-supporting pleatedfilter. The filter media has a plurality of pleats defining a pluralityof pleat tips and sloping side surfaces extending along a front face anda rear face. The pleat tips extend perpendicular to a direction ofpleating. A planar reinforcing strip oriented in the direction ofpleating is bonded to the pleat tips along the front face of the pleatedfilter. A reinforcing structure is provided along the rear face of thepleated filter. A frame optionally extends around the perimeter of thefilter media. In another embodiment, the pleated filter may be insertedinto, and subsequently removed from, a reusable frame.

In one embodiment, the reinforcing structure includes one or morereinforcing members extending in the direction of pleating generallyalong the contour of the pleat tips and sloping side surfaces of therear face. In one embodiment, the reinforcing members are bonded to thefilter media. A generally planar second reinforcing strip oriented inthe direction of pleating is bonded to reinforcing member pleat tips onthe pleated reinforcing member. In one embodiment, the reinforcingmember, the first reinforcing strip and the second reinforcing strip arepositioned to define a truss structure.

In another embodiment, the reinforcing structure includes at least onereinforcing member oriented perpendicular to the direction of pleatingthat is positioned generally along at least one of the sloping sidesurfaces of the rear face. In one embodiment, the frame extends overdistal ends of the reinforcing member. The reinforcing member may alsobe bonded to the filter media.

In another embodiment, the reinforcing structure includes a scrim thatextends over the rear face of the pleated filter. In one embodiment, aportion of the frame extends over a perimeter of the scrim and onto therear face of the filter media.

In another embodiment, a scrim is substituted for the reinforcing striplocated along the front face. The scrim is bonded to the pleat tips onthe front face to form a pleated filter. Any of the reinforcing membersdisclosed herein can be used along the rear face of the pleated filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system for performing the methodof the present invention.

FIG. 2 is a perspective view of a self-supporting pleated filter inaccordance with the present invention.

FIG. 3 is a top schematic illustration of one embodiment of the methodof the present invention.

FIG. 4 is a top schematic illustration of an alternate method inaccordance with the present invention.

FIG. 5 is a sectional view of a self-supporting pleated filter inaccordance with the present invention.

FIG. 6 is a side sectional view of the pleated filter of FIG. 5.

FIG. 7 is a side sectional view of an alternate reinforcing member inaccordance with the present invention.

FIG. 8 is a side sectional view of an alternate reinforcing member inaccordance with the present invention.

FIG. 9 is a side sectional view of an alternate reinforcing member inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic illustration of a system 20 for performing themethod of the present invention. Filter media 22 is typically providedon a continuous roll 24. The media 22 may be slit to the desired widthat slitting station 26. The media 22 may optionally be preheated at aheating station 28 to facilitate processing. In the illustratedembodiment, the heating station 28 is an infrared heater.

In one embodiment, a reinforcing member 30 is applied to a rear face 32of the media 22 at a location 34. As will be discussed in detail below,the reinforcing member 30 may be applied as one or more continuousstrips oriented in the direction of pleating 36, as discrete reinforcingmembers oriented perpendicular to the direction of pleating 36, or avariety of other configurations. The reinforcing member 30 mayoptionally be bonded to the media 22 using a variety of techniques, suchas adhesive bonding, thermal bonding, solvent bonding, or ultrasonicbonding. In this embodiment, the location 34 is upstream of rotary-scorepleater 38 that scores the media 22 and the reinforcing member 30 priorto pleating. The rotary-score pleater 38 and pleat folding station 40may be modified to accommodate the increased thickness in the filtermedia 22 at the location of the reinforcing member 30.

The assembly of the media 22 and the reinforcing member 30 is advancedthrough the rotary-score pleater 38 to a pleat folding station 40.Infrared heaters 42 may optionally be provided for heat-setting thepleats 44. The pleats 44 are retained in an accumulator 46 until beingadvanced to a pleat spacing device 48 that retains the pleats 44 in thedesired pleat spacing. Pleat formation and pleat spacing may beperformed by a variety of methods, such as disclosed in U.S. Pat. No.4,798,575 (Siversson); U.S. Pat. No. 4,976,677 (Siversson); and U.S.Pat. No. 5,389,175 (Wenz).

The pleated filter media 60 is expanded to the desired pleat spacing inthe pleat spacing device 48. One or more elongated, planar reinforcingstrips 62 are applied to the pleat tips along the front face 64 at thestation 68 to maintain the pleat spacing. The reinforcing strips 62 canbe bonded to the pleat tips by various techniques, such as adhesivebonding, thermal bonding, solvent bonding, or ultrasonic bonding. Thepleated filter media 60 and the reinforcing strip 62 define a pleatedfilter 72 that can be cut, machined handled or otherwise processed. Thereinforcing strips 62 provide dimensional stability to the pleats 44 ofthe pleated filter 72. The pleated filter 72 can be used in filtrationapplications, with or without a frame structure, or as an insert into apermanent/reusable frame.

In another embodiment, a scrim 62 extending substantially across theentire front face 64 is substituted for the planar reinforcing strips62. The scrim is bonded to the pleat tips to provide dimensionalstability to the pleated filter 72. Use of a scrim 62 extending acrossthe front face 64 may be used in combination with any of the reinforcingmembers discussed herein.

In the illustrated embodiment, one or more elongated, planar reinforcingstrips 66 are optionally bonded to the rear face 32 of the pleatedfilter media 60 at the station 68. In one embodiment, the reinforcingstrips 66 are located over the reinforcing member 30 and opposite thereinforcing strips 62 to form truss structures (see FIG. 6).

In one embodiment, a continuous strip of frame material 80 is applied tothe ends of the pleated filter media 60 parallel to the direction ofpleating 36. An adhesive, such as a hot melt adhesive, is applied to afirst flange of a U-shaped channel formed from the frame material 80 atthe station 87. The adhesive for sealing the ends of the pleats 44 isapplied at station 88. A hot melt adhesive is applied to the secondflange of the U-shaped channel at station 90. The frame material 80 isbent into its U-shaped configuration at station 94. The ends U-shapedchannel extend partially onto the front face 64 and rear face 32 of thepleated filter media 60 (see FIG. 5). An assembly including the endlessweb of pleated filter media 60 and attached frame material 80 is cut atstation 86 to desired lengths. Alternatively, the pleated filtercomprising the pleated filter media 60 and the reinforcing strips 62 canbe cut to size before application of the frame material 80.

The pleated filter media 60 and side frames members 92 are rotated 90°at location 91 to permit application of the end frame members 96 at astation 98. Alternatively, the frame members 92, 96 can be configured astwo box structures that are positioned over the first and second faces32, 64, respectively, of the pleated filter 72, with overlappedcircumferential portions, such as disclosed in U.S. Pat. No. 5,782,944(Justice). In another embodiment, the frame member members 92, 96 can beconfigured as a one-sided die-cut frame that is folded around thepleated filter 72.

In embodiments where the pleated filter media 60 is used without framemembers 92, 96, the pleated filter 72 exits the system 20 after thecutting station 86. Alternatively, a pleated filter 100 with a frame(see FIG. 2) exits the system 20. The pleated filters 72, 100 aretypically enclosed in suitable packaging.

Pleat spacing is typically about 3 to about 6 pleats per 2.54centimeters (1 inch). Pleat depth and the thickness of the filter 100 istypically about 2.54 centimeters to about 101.6 centimeters (1 inch to 4inches). For HVAC applications, the length and width of the filter 100is typically 30.5 centimeters×30.5 centimeters (12 inches×12 inches) toabout 50.8 centimeters×76.2 centimeters (20 inches×30 inches). Referenceto the front face 64 or rear face 32 is for purposes of description onlyand does not indicate an orientation of the pleated filter 100. Forexample, the reinforcing member 30 may be positioned upstream ordownstream in the air flow.

The resulting pleated filter 100 in accordance with the presentinvention is self-supporting. A pleated filter is self-supporting asdefined herein when the portion of the pleats 44 that are not directlysupported by the reinforcing member 30 or the reinforcing strips 62, 66do not collapse or bow excessively when subjected to the air pressuretypically encountered in forced air ventilation systems.

Stiffness of the filter media 22 is a factor in determining thesuitability of a particular filter media for use in the presentinvention. A Taber V-5 Stiffness Tester, Model 150-B, made by TeledyneTaber of North Tonawanda, N.Y., can be used to evaluate the stiffness ofthe filter media. The V-5 stiffness tester operates by bending aspecimen about 38.1 millimeters wide by about 38.1 millimeters long (1.5inches by 1.5 inches) to a prescribed angular of deflection andmeasuring the force, in stiffness units ranging from 0-10, used toobtain this deflection. In many heating, ventilating and airconditioning (HVAC) applications, the air pressure is generally about125 Pa to about 249.1 Pa (0.5 to 1.0 inch column of water) and the facevelocity is approximately 91.5 meters per minute (300 feet per minute).For HVAC filtration applications, the minimum stiffness value is greaterthan about 1.2 stiffness units, and preferably greater than about 1.5stiffness units and more preferably greater than about 2 stiffnessunits.

The U-shaped channel of the side frame members 92 serve to furtherstabilize the pleated filter media 60 and to seal the ends of the pleats44 to prevent air bypass in the final pleated filter 100. In oneembodiment, a viscous adhesive such as a foamed adhesive, a filledadhesive or a caulk is used to seal the ends of the pleats 44 to theframe members 92, 96. Latex caulk is well suitable for this purposesince it is low cost and has low volatile organic content. On the otherhand, latex caulks have a long set time. Therefore, other adhesives,such as hot melt adhesives, are utilized to bond the two sides of theU-shaped channel formed from the frame material 80 to the pleat tips 44.A variety of techniques may be used for applying the frame members 92,96 to the pleated filter, such as disclosed in U.S. Pat. No. 4,731,047(Lobb).

FIG. 3 is a top schematic illustration of one embodiment of the presentmethod for making a self-supporting pleated filter. The reinforcingmember 30 is oriented in the direction of pleating 36 along the rearface 32. In one embodiment, the reinforcing member 30 is bonded to thefilter media 22. In the illustrated embodiment, the reinforcing member30 is strips about 0.64 centimeters to about 2.54 centimeters (0.25inches to about 1 inch) wide. The filter media 22 and reinforcing member30 are subject to a pleating operation at station 40, resulting inpleats being formed in the reinforcing members 30. The pleatedreinforcing members 30 include reinforcing member pleat tips 120.

The reinforcing strip 62 is applied to the front face 64 of the pleatedfilter media 60 at the station 68 to form the pleated filter 72 (seeFIG. 1). The reinforcing strip 66 is also bonded to the reinforcingmember pleat tips 120 at the station 68. The reinforcing strips 62, 66provide added dimensional stability to the pleated filter media 60 tofacilitate machine handling. Frame material 80 is optionally applied tothe edges of the pleated filter media 60 parallel to the direction ofpleating 36 to form side frame members 92, as previously discussed. Thecombination of the pleated reinforcing member 30, the reinforcing strips66 along the rear face 32 and the reinforcing strip 62 along the frontface form a truss structure that gives the pleated filter media 60 itsself-supporting properties (see FIG. 6). The pleated filter media 60 andframe material 80 are cut to length at the cutting station 86.Alternatively, the pleated filter 72 can be cut to size prior toapplication of the frame material 80.

FIG. 4 is a top schematic illustration of an alternate method inaccordance with the present invention. The reinforcing member 30 isapplied to the media 22 at discrete locations along the rear surface 32perpendicular to the direction of pleating 36. The reinforcing member 30may optionally be bonded to the filter media 22. The assembly of thefilter media 22 and the reinforcing member 30 is subject to the pleatingoperation at the station 40 so that the reinforcing member 30 issimultaneously pleated with the filter media 22.

The reinforcing strip 62 is applied to the front face 64 of the pleatedfilter media 60 at the station 68 to form the pleated filter 72 (seeFIG. 1). Reinforcing strips 66 are optionally applied to the pleat tipsalong the rear face 32 at the station 68. In the embodiment illustratedin FIG. 4, the side frame members 92 preferably extend onto the rearface 32 of the pleated filter media 60 so that stresses imposed on thereinforcing members 30 are transmitted to the frame members 92.

Turning back to FIG. 1, the reinforcing member 30 may optionally beinserted directly into the pleated filter media 60 at a station 70. Thereinforcing member 30 can be preformed to correspond to the pleat tipsand sloping side surfaces of the pleats 44 (see FIG. 7). The reinforcingmember 30 may optionally be bonded to the pleated filter media 60. Inone embodiment, the station 70 is located upstream of the station 68where the reinforcing strip 66 is applied to the rear face 32. In thisembodiment, the reinforcing strip 66 helps to retain the reinforcingmember 31 to the pleated filter media 60. Alternatively, the reinforcingmember 30 may be inserted into the pleats of the pleated filter media 60at station 70′ located downstream of the station 68.

The reinforcing member 30 may be a scrim extending across the rear face32 prior to forming the frame members 92, 96. The stations 70 or 70′ maybe used to position a scrim along the rear face 32. The scrim mayoptionally be adhesively bonded to the pleated filter media 60. In thisembodiment, the reinforcing strip 62 will be applied to the front face64 to maintain pleat spacing and facilitate machine handling, but thereinforcing strip 66 along the rear face 32 may be unnecessary.

The filter media 22 may be paper, porous films of thermoplastic orthermoset materials, nonwoven webs of synthetic or natural fibers,scrims, woven or knitted materials, foams, or electret orelectrostatically charged materials. The filter media 22 may alsoinclude sorbents, catalysts, and/or activated carbon (granules, fibers,fabric, and molded shapes). Electret filter webs can be formed of thesplit fibrillated charged fibers as described in U.S. Pat. No. RE30,782. These charged fibers can be formed into a nonwoven web byconventional means and optionally joined to a supporting scrim such asdisclosed in U.S. Pat. No. 5,230,800 forming an outer support layer.Alternatively, the filter media 22 can be a melt blown microfibernonwoven web, such as disclosed in U.S. Pat. No. 4,817,942 which can bejoined to a support layer during web formation as disclosed in thatpatent, or subsequently joined to a support web in any conventionalmanner. The reinforcing member 30 and the reinforcing strips 62, 66 maybe constructed from various paper products, polymeric materials, ormetals. These materials can be configured as strips, films, scrims,strands or filaments. The frame members are typically paper products,such as chipboard, or polymeric materials.

FIGS. 5 and 6 illustrate a self-supporting pleated filter 200 thatcorresponds with the method illustrated in FIG. 3. The pleated filtermedia 60 is retained within a pair of opposing side frame members 92 andend frame members 96. The reinforcing member 30 of FIG. 3 correspondsgenerally to the reinforcing member 202 that extends in the direction ofpleating 36 and generally follows the contour of the pleat tips 204 andsloping side surfaces 206, 208. That is, the reinforcing member 202extends into the pleats along the z-axis. The z-axis is the axisperpendicular to a plane defined by the front face 64 or the rear face32 of the pleated filter media 60. The reinforcing member 202 has aplurality of reinforcing member pleat tips 210. Reinforcing strip 66 isoptionally bonded to the reinforcing member pleat tips 210 along therear face 211. Reinforcing strip 62 is oriented in the direction ofpleating 36 and bonded to the pleat tips 204 along the front face 212and opposite the reinforcing member 202 to form a truss structure.

FIG. 7 is a perspective view of an alternate self-supporting pleatedfilter 230 that corresponds generally to the method illustrated in FIG.4. The reinforcing member 30 corresponds generally to the reinforcingmember 232. The reinforcing member 232 extends into the pleats along thez-axis, perpendicular to the rear face 32. The reinforcing member 232can be bonded to the pleated filter media 60, retained by the side framemembers 92, or a combination thereof. The reinforcing strip 66 mayoptionally be provided along the rear face 32. In the illustratedembodiment, the reinforcing member 232 has a V-shape that extends alonga pair of opposing side surfaces 234, 236 of two pleats 238. In analternate embodiment, the reinforcing structure 232 extends across asingle pleat. In one embodiment, the reinforcing member 232 is a metalscrim.

FIG. 8 illustrates an alternate reinforcing structure 250 that isdeposited in the pleats 252, rather than being pleated with the filtermedia 60. The reinforcing structure 250 is typically inserted into thepleats 252 of the pleated filter media 60 prior to application of theoptional reinforcing strip 66. In the embodiment illustrated in FIG. 8,the reinforcing structure 250 extends along a single pleat 252 andincludes side extensions 254 that extend parallel to the rear face 32over additional pleats. In order to minimize pressure drop across thepleated filter media 60, the reinforcing structure 250 is a porousmaterial, such as a scrim. The reinforcing structure 250 may be retainedto the pleated filter media 60 by bonding, by the optional reinforcingstrip 66 and/or by the side frame members 92. In an alternateembodiment, the reinforcing structure 250 has a triangular shapecorresponding to the shape of the pleats 252.

FIG. 9 illustrates an alternate pleated filter 270 with a continuousreinforcing structure 272 extending across the rear surface 32 of thefilter media 60. Reinforcing strips 62 are located along the front face64 (see FIG. 1). Reinforcing strip 66 is optionally provided on the rearface 32 over or under the reinforcing structure 272. The reinforcingstructure 272 may be retained to the pleated filter media 60 by bondingto the frame members 92, 96 and/or the filter media 60, by the optionalreinforcing strip 66 and/or by the side frame members 92. The continuousreinforcing structure 272 may be a scrim, mesh, screen or other porousmaterial. In an alternate embodiment, the continuous reinforcingstructure 272 is bonded to the pleat tips along the front face 64 inplace of the reinforcing strips 62.

The complete disclosures of all patents, patent applications, andpublications are incorporated herein by reference as if individuallyincorporated. Various modifications and alterations of this inventionwill become apparent to those skilled in the art without departing fromthe scope and spirit of this invention, and it should be understood thatthis invention is not to be unduly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A self-supporting, pleated filter, comprising:(a) a web of electronically charged filter media having a stiffness ofat least 1.2 stiffness units formed into a plurality of pleats defininga plurality of pleat tips and sloping side surfaces extending along afront face and a rear face, the pleat tips being perpendicular to adirection of pleating; and (b) a reinforcing structure comprising: (i) afirst generally planar scrim bonded in the pleat tip across the frontface; and (ii) a second generally planar scrim bonded to the pleat tipsacross the rear face such that the first planar scrim, the second planarscrim and the pleats comprise a truss structure that provides thepleated filter with self-supporting properties; wherein each of saidfirst and said second scrims is a metal screen.
 2. A self-supporting,pleated filter as defined in claim 1, further comprising a frameextending around the perimeter of the filter media and onto a portion ofsaid front face and said rear face of said filter media.
 3. Aself-supporting, pleated filter as defined in claim 1, wherein saidperimeter of said filter media is adhesively bonded to said frame.
 4. Aself-supporting, pleated filter as defined in claim 3, wherein saidfileter media has about 3 to about 6 pleats per 2.54 centimeters (1inch).
 5. A self-supporting, pleated filter as defined in claim 4,wherein each said pleat has a depth of about 2.54 centimeters to about10 to bout 101.6 centimeters (1 inch to 4 inches).